Degreasing machine with cooling jacket



3 Sheets-Sheet 1 INVENTOR.

M. B. PICKETT 4 DEGREASING MACHINE WITH COOLING JACKET Feb. 11, 1958Filed Sept. 9. 1953 Feb. 11, 1958 Filed Sept. 9, 1953 M. B. PICKETTDEGREASING MACHINE WITH COOLING JACKET 5 Sheets-Sheet 2 I Q/ 39 7SINVENTOR.

ameyfiz zdeii, 2 BY Feb. 1 1, 1958 M. B. PICKETT DEGREASING MACHINE WITHCOOLING JACKET 3 Sheets-Sheet 3 Filed Sept. 9, 1953 lllllllllllllllllillfllirllllz I Mama United States Patent DEGREASING MACHINE WITHCOOLING JACKET Montgomery B. Pickett, Glen Ellyn, 11]., assignor to S.Blakeslee & Co., Cicero, 111., a corporation of Illinois ApplicationSeptember 9, 1953, Serial No. 379,132

4 Claims. (Cl. 202170) This invention relates to degreasing machinesemploying a heated volatile solvent for receiving the articles to becleansed and provided with a cooling zone for condensing the vaporsarising from the heated volatile solvent and returning the condensate tothe body of liquid. Machines of this general type are well known and arecommonly employed for cleaning metal parts of grease, dirt, wax and thelike, so as to produce a chemically clean surface for the purpose ofpreparing the articles for subsequent operations.

Trichlorethylene is extensively used in degreasing machines. It has aboiling point of around 200 F. and the vapor is several times heavierthan air. In order to prevent the escape of solvent vapors from the tankor container in which the degreasing operations are carried out, it iscustomary to provide cooling means at the upper portion of the tank forchilling and condensing the vapors so as to prevent them from passingthe chilled zone and i the cooling means through which the tap water isdirected s is sufiiciently low that water vapors from the atmosphere, aswell as the solvent vapors from the tank, are condensed by the coolingmeans, becoming mixed with the solvent condensate, and are returned tothe tank along with the condensate of the solvent.

The addition of water to the solvent in any appreciable quantitymaterially reduces the boiling point of the solvent, which isobjectionable. Further, the tank or container of a degreasing machineusually is constructed of sheet steel and is suitably coated to guardagainst rusting and contamination of the solvent. In machines providedwith a cooling jacket extending about the upper portion of the tank, itis common practice to secure the jacket to the tank wall by stay boltsextending between the tank wall and the jacket. If water vapor ispresent in appreciable amount in the solvent vapor, the condensate willcontain water which can give rise to the presence of hydrochloric acid.As the condensate flows down the inner face of the wall of the tank, ittends to collect on the heads of the stay bolts and, if hydrochloricacid is present, the protective coating may be rapidly eaten away-andrusting of the wall of the tank about the heads of the stay boltsoccurs. Further, as the condensate flows down the inner face of the tankwall, it it contains water in appreciable amount the hydrochloric acidmay quickly eat away the protective coating thus exposing the sheetsteel wall which rapidly becomes rusted or corroded. In cases where thetank or container is constructed of stainless steel, or stainless cladmetal, it may be attacked by hydrochloric acid if present in substantialamount or for extended periods of. time.

My invention is directed to a degreasing machine having a cooling jacketstructure associated with thetank wall.

in a novel manner eliminating the necessity for using stay bolts whileproviding effective reinforcement for the jacket structure, and for thecorresponding area of the wall of the tank. To that end, I provide ajacket structure extending about the tank and provided with channelmeans which imparts desired rigidity and strength to the jacketstructure while also effectively reinforcing the corresponding area ofthe tank wall so as effectively to prevent distortion or warping of thelatter under changing operating conditions and temperature variations.The channel means provides, in conjunction with the remainder of thejacket structure and the wall of the tank, passages extending about thetank and through which a suitable coolant, conveniently tap water, iscirculated. The passages of the jacket structure may be connected bysuitable means establishing communication between them. The jacketstructure is provided with coolant inlet and outlet connectionsand maybe further provided with baffles disposed to cause flow of coolantthrough the passages in desired manner. Further objects and advantagesof my invention will appear from the detail description.

In the drawings:

Figure 1 is a side view of a degreasing machine embodying the coolingjacket of my invention; I I

Figure 2 is a top plan view of the machine of Figure 1;

Figure 3 is an end view of the machine of Figure 1;

Figure 4 is an enlarged fragmentary side view of the upper portion ofthe machine including the cooling jacket;

Figure 5 is a sectional view taken substantially on line 5-5 of Figure4;

Figure 6 is a sectional view taken substantially on line 6-6 of Figure4;

Figure 7 is a view simila to Figure 4 but showing. a modification;

Figure 8 is a sectional view taken substantially on line 88 of Figure 7;

Figure 9 is a sectional view taken substantially on line 9-9 of Figure7;

Figure 10 is a sectional view taken substantially on line 10-10 ofFigure 7;

Figure 11 is a sectional view similar to Figure 10 but showing a secondmodification;

Figure 12 is a sectional view similar to Figure 10 but showing a thirdmodification;

Figure 13 is a sectional view similar to Figure 10 but showing a fourthmodification; and

Figure 14 is a sectional view similar to Figure 10 but showing a fifthmodification.

The degreasing machine to which the cooling jacket of my invention isapplied is, in general, of known construction and operation and a briefdescription thereof will suflice. The machine comprises a tank 10constructed of sheet steel, which is galvanized or otherwise providedwith a protective coating to guard against corrosion or rusting. Thelower portion of tank 10 is separated into two compartments 11 and 12.The number of compartments within the tank may be varied, as is known,two compartments being shown by way of example only. The compartment 11contains liquid solvent, such as trichlorethylene, which extends towithin a short distance of the top of the compartment. This compartmentis provided with a false bottom 13 of open construction and with abottom 13a with a space or sump therebetween. A neck 14 extendsoutwardly from the sump and normally is closed by a clean-out door 15removably secured, conveniently by bolting, to a flange 16 of neck 14. Asteam heating coil (not shown) may be carried by the door 15 anddisposed so as to be positioned within the sump,.this coil having endconnections or nipples 17 and 18 extending outward therebeyond forconnection to a suitable source of supply of steam. Additional heatingmeans, in the form of gas burners (not shown) may be disposed beneathbottom 13a of comparb ment 11, the burners being connected by piping 20to a suitable source of supply of gas, the piping including valves 21for controlling the individual burners. The bottom of compartment 12 isclosed by a bottom wall 22 and this compartment is filled with liquidsolvent, such as trichlorethylene. A pipe 23, provided with suitablevalves 24 and 25, is connected to the bottom of compartment 12 and tothe bottom of the sump of compartment 11, for draining the compartmentsas necessary or desired.

The tank is open at its top and is provided with an outer peripheralflange 26 upon which may be mounted sliding covers (not shown) forclosing the top of the tank. A condensate trough 27 extends about theinterior of tank It a substantial distance above the liquid level of thesolvent in the compartments 11 and 12. This trough receives condensateflowing down the inner face of the wall of the tank and conducts thecondensate, by means of pipe 23, cooler 29 and pipe 39 to a waterseparator 31 of known type. The trichlorethylene, which is heavier thanwater, is separated by gravity from the water contained in thecondensate delivered from trough 27 to separator 31, the separated waterbeing discharged from separator 31 through pipe 32 and thetrichlorethylene being returned to compartment 12 through pipe 33. Thesubstantially pure trichloroethylene overflows from compartment 12 intocompartment ll for replenishing the trichlorethylene in the lattercompartment. A flue 2th: is connected to the burner chamber beneathcompartment 11, for taking off the products of combustion. Thedegreasing machine so far described, including the condensate trough 27,cooler 29 and separator 31, is of known construction and need not bedescribed in further detail, except insofar as relates to my instantinvention.

In. the use of the machine. the articles to be cleaned are immersed inthe hot trichlorethylene in compartment 11, heated to its boiling point.Thereafter the articles are rinsed in the compartment 12 by beingimmersed in the substantially pure and uncontaminated trichorethylenetherein, and are then raised into a vapor zone, between the surface ofthe liquid trichlorethylene and cooling means disposed above the trough27, this vapor zone being filled with the solvent vapor generated incompartment 11 by heating the trichlorethylene therein.

The rinsed articles may be held in the vapor zone so as to be furthercleansed by the action of the vapor which condenses on the articles, thelatter being cooled by dipping in the unheated solvent in compartment12. Alternatively, the articles may be raised fi'oinconipai'tment 12directly into a cooled zone above the vapor zone, in which cooled Zonethe articles quickly dry. The cooled zone is provided by cooling means,with which my invention is particularly concerned and which will now bedescribed in detail.

A cooling jacket 35 extends about the tank 10 a short distance above thecondensate trough 27. The jacket 35 is provided with top and bottomwalls 36 and 37, respectively, which seat on and are suitably secured,conveniently by welding, to the wall a of the tank 10. Jacket 35 also isprovided, at about its mid-height, with a channel element 33 extendinginward from the outer side wall 39 thereof, channel member 38 beingpreferably of fiattened V-shape in cross section and seating on the wall1th! of tank 10, to which it is suitably secured, conveniently by spotwelding as indicated at 40. The channel member 38 preferably is formedintegrally with the outer side Wall 39 of jacket 35 by being pressedinwardly therefrom though within the broader aspects of my invention thechannel member 33 may be formed in any other suitable manner. The jacket35, in conjunction with the wall 164: of tank 16 and channel member 38,provides two passages extending about the tank, as will be clear fromwhat has been said. Additionally, the channel member 38 impartsdesirable rigidity to the jacket 35 and-t0 thecorresponding area of thewall 10a of tank 10 so as to resist buckling or deformation of that wallunder temperature variations.

The channel member 38 is interrupted, conveniently at one corner of thejacket 35, by a duct 42 bridging channcl member 38 and providingcommunication between the upper and lower passages 43 and 44,respectively, of the jacket 35. The duct 42 is shown more clearly inFigures 4 and 5, and is provided by two plates 45 and 46 extendingbetween the wall 19a of tank 10 and the outer side wall 39 of jacket 35and welded thereto, plate as being at the inner face of a bathe 47aligned with one end wall of tank 10 and closing the lower passage 44 ofjacket 35. A connection, in the form of a nipple 48, opens into passage44 at the bottom thereof and at the opposite side of baffie 47 from theduct 42. A bathe St) is disposed at the outer face of plate 45 andcloses the upper passage 43 of jacket 35 at the opposite side of duct 42from the baffle 47. A coolant'connection, in the form of a nipple 52,opens into passage 43 at the top thereof, at the opposite side of battle59 from the duct 42. it will be clear, from What has been said, thatcoolant, conveniently tap water, entering the jacket 35 through one ofthe connections 48 or 52 will flow through one of the passages of thejacket around the tank 10 and then through the duct 42 into the otherpassage and through the latter passage around the tank and thencethrough the other connection. It may be assumed, for purposes ofdescription, that the water enters through the nipple 48. The waterwillthen flow through passage 44 around the tank to the duct 42 and throughthe latter to passage 43 and through the latter passage and around thetank to nipple'52, from which the water flows through a pipe 54 to asuitable point of discharge. Preferably, though not necessarily, thecooling water is delivered to the jacket 35 from the cooler 29, througha pipe 55 from the outlet of the cooler, the inlet of the cooler beingconnected by a pipe '56 to a suitable source of supply of cooling water,as will be understood. The water flowing through cooler 29 absorbs acertain amount of heat from the condensate being delivered to theseparator 31, which is advantageous as guarding against ebullition orboiling of the condensate in the water separator 31, which wouldinterfere with gravity separation of the solvent and the water. Further,by preheating to a certain extent the water entering the cooling jacket35, I guard against objectionably low temperatures in the cooling zonesuch as might result in condensation of water vapor with the solventvapors, which is objectionable for reasons previously explained.

Whilethe jacket of Figures 1 to 6, inclusive, provides efiicient coolingmeans suitable for use under normal conditions, if used in an atmosphereof high humidity there might be a tendency to condense water vapor withthe solvent vaporsl which is objectionable for the reasons stated. InFigures 7 to 9, inclusive, I have shown a modified form of coolingjacket which is suitable for use under conditions of high humidity. Thisform of jacket is in general similar to that of Figures 1 to 6,inclusive, except as to the arrangement of the bafiling. Referring toFigure 7, it will be noted that the upper passage 43 of the water jacket35 i's provided with a baffie 5001 as a continuation of the baffle 47 inthe lower passage 44, bafiie 50a closing the passage 43. This latterpassage 43 is further provided with a second bafl le 54a at the side ofduct 42 opposite to baffles'47 and'50a, the bafile 54a terminating shortof the top wall of passage 43 and closing this passage except for thetop opening thus provided. The lower passage 44 is also provided with asecond baffle 45a constituting a downward extension of the inner sideplate of the duct 42, this baffle 45a terminating short" of the-bottomwall of passage 44 and closing the latter passage except for theopeningthus provided. The upper'passage 43 is provided'with a coolantconnection or nipple 52a at the top thereof and "at'the opposite side ofthe bafile 50a from the duct 42. The lower passage 44 is also providedwith a coolant connection or nipple 48a at the top thereof and at theopposite side of the baflie 47 from the duct 42. In practice, the nipple52a is connected to the pipe 55 so that the water flows from the cooler29 into passage 43 of the jacket 35 and through this passage around thetank to the baffle 54a, over which the water passes downward throughduct 42 into passage 44 and beneath the baflle 45a, flowing throughpassage 44 about the tank in the reverse direction to which it flowedthrough the passage 43, the water then being discharged through thenipple 48a. By flowing the water through the jacket in the manner justdescribed, the water, in addition to being preheated to a certain extentby flowing through the cooler 29, is heated during its flow through theupper passage 43 by heat absorbed from the tank wall at the upperportion of the cooling zone, so that when the water enters the lowerpassage 44 it is at a higher temperature than when it enters the upperpassage. Accordingly, the area of the tank wall corresponding to thelower passage 44 is not abruptly cooled to an objectionably lowtemperature, and the area of the tank wall 10a corresponding to thejacket is cooled to a more nearly uniform temperature somewhat higherthan the temperature to which the area of the tank wall corresponding tothe lower passage 44 is cooled in the form of jacket shown in Figures 1to 6, inclusive. The top of the vapor zone is at about the center of thewater jacket, preferably a little lower, and in either of the two formsof jacket shown the solvent vapor is condensed on the inner face of thetank wall 10a and flows down the latter into the condensate trough 27.By preheating the cooling water and passing it through the jacket 35from the top to the bottom thereof, in the form of jacket shown inFigures 7 to 9, inclusive, cooling of the tank wall 10a to such anextent as to condense water vapor with the solvent vapor inobjectionable amount is avoided to large extent. That eliminates, orgreatly reduces, risk of the formation of hydrochloric acid, thuspreventing or greatly reducing removal of the protective coating andresultant corrosion and rusting of the wall of the tank. In both formsof jacket illustrated, stay bolts or equivalent means for mounting thejacket are avoided, thus avoiding the risk of corrosion about the headsof such members. Further, the channel member of the jacket welded to thetank wall provides effective stiffening and reinforcing means thereforand for the jacket and avoids buckling or distortion of the tank walldue to temperature variations. By forming the channel member as anintegral part of the jacket, the jacket as a whole may readily befabricated at comparatively low cost and may also be mounted and securedupon the tank at low cost, which is conducive to low cost of productionof the degreasing machine.

I In the modification shown in Figure 11, the outer side wall 39a of thejacket 35a is flat and a channel member 38a is pressed out from thetank'wall 10b and seats on the inner face of wall 39a of the jacket 35a,to which it is spotwelded. That provides the upper and lower passages 43and 44 for flow ofcoolant about the tank wall. By pressing the rib orchannel member 38a outward from the tank wall 10b,'the cooling area ofthat wall is increased to a substantial extent, which is desirable incertain cases. It will be noted that the lower arm of the channel member38a is inclined downward and inward of the tank so that any condensatecollecting in the channel 38a will readily drain therefrom into thetank. The channel member 38a effectively reinforces the tank wall 10band the wall 39a of the jacket 35a and imparts desirable rigiditythereto with the advantages previously described.

The modified form shown in Figure 12 is similar to that shown in Figure11, except that a plurality of channel members 38b are pressed out fromthe tank wall 10c further increasing the cooling area of that wall andproviding a plurality of channels v49 extending about the tank. As willbe understood from what has been said, the passages 49 may beinterconnected by suitably disposed ducts similar to the duct 42 shownin Figures 1 to 6, inclusive. Also, suitably arranged baffles may beprovided in the passages 49, if desired. Further, inlet and outletconnections for the coolant may be provided, such connections beingdisposed to cause flow of coolant through the passages 49 as desired.

In the modified form shown in Figure 13, the jacket 35b is mounted onthe inner face of the tank wall 10a and is provided with a plurality ofchannel members 380 pressed therefrom and extending outward to the tankwall 10a, seating thereon and being spot welded thereto. The jacket 35b,in cooperation with the tank wall 10a, provides a plurality of passages51 for flow of coolant about the tank. Suitable coolant connections tothe passages 51 may be provided and these passages may be connected bysuitably disposed ducts. The channel members 38c provide increasedcooling area at the inner side of the tank wall, as will be clear, insubstantially the same manner as the channel members 38b of Figure 12.Further, in both Figures 12 and 13, the channel members provideeffective reinforcing and thus stiffening means for the jacket and thewall of the tank.

In the modified form shown in Figure 14, the tank wall 10d is providedwith a plurality of channel members 38c pressed outwardly therefromalternating with inwardly pressed channel members 38d, and a flat plate53 is welded to the outer face of wall 10d closing the outer sides ofthe channel members 38d, the channel members 380 seating on the plate 53and being welded thereto. The plate 53 thus cooperates with the channelmembers 380 and 38d to provide a jacket structure defining passages 51aextending about the wall of the tank. The passages 51a may be connectedby suitable ducts and have associated therewith suitably dispose-dcoolant inlet and outlet connections providing for flow of coolantthrough the passages 51a in desired direction. The channel members 38cand 38d together constitute the cooling jacket closed at its outer sideby the plate 53 and also effectively reinforce the tank wall 10d andimpart desired rigidity thereto and to the plate 53.

It will be understood from the above that changes in detail may beresorted to without departing from the field and scope of my invention,and I intend to include all such variations, as fall within the scope ofthe appended claims, in this application in which the preferred formsonly of my invention have been disclosed.

I claim:

1. In degreasing apparatus, a tank having an enclosing wall and adaptedto contain a degreasing solvent and vapors thereof, cooling jacket meansextending about said tank exteriorly and remote from the bottom thereof,said jacket means comprising upper and lower channel elements and anintermediate channel element fixed to said upper and lower elements andto the tank wall, said upper and lower channel elements being closed atthe inner sides thereof by the corresponding portions of the tank walland defining therewith upper and lower passages extending substantiallycompletely about said tank and having an inner wall of substantial areaexposed interiorly of said tank, said channel elements being rigidlyconnected together and to said tank wall effective for reinforcing thelatter, a duct bridging said intermediate channel element andestablishing communication between said passages, each of the latterhaving a coolant connection at the area thereof adjacent said duct, andbafiie means in said passages eifective for causing coolant entering oneof said passages to flow therethrough in one direction around said tankto said duct and through the latter to the other passage and thenthrough said other passage in the opposite direction around the tank tosaid coolant connection of said other passage, whereby the coolantflowing through said one passage is preheated by heat absorbed from thesolvent vapors within the tank before it enters said other passage.

2. In degreasing apparatus, a tank having a fiat wall and adapted tocontain a degreasing solvent and vapors thereof, cooling jacket meansextending about said tank exteriorly and remote from the bottom thereof,said jacket means comprising upper and lower channel elements and anintermediate channel element fixed to said upper and lower elements andto the wall of said tank, said elements being of substantiallyrectangular cross section and directed alternately inwardly andoutwardly of said tank, said upper and lower elements being closed atone side thereof by the corresponding portions of the tank wall anddefining therewith upper and lower passages of substantially rectangularcross section extending substantially completely about said tank andhaving fiat walls of substantial area exposed interiorly of said tank,said channel elements being rigidly connected together and to'said tankwall effective for reinforcing the latter, a duct bridging saidintermediate channel element and establishing communication between saidpassages, each of the latter having a coolant connection at the areathereof adjacent said duct, and baffle means in said passages effectivefor causing coolant entering one of said passages to flow therethroughin one direction around said tank to said duct and through the latter tothe other passage and then through said other passage in the oppositedirection around the tank to said coolant connection of said otherpassage, whereby the coolant flowing through said one passage ispreheated by heat absorbed from the solvent vapors within the tankbefore it enters said other passage.

3. In degreasing apparatus, a tank having a fiat wall and adapted tocontain a degreasing solvent and vapors thereof, cooling jacket meansextending about said tank exteriorly and remote from the bottom thereof,said jacket means comprising upper and lower channel elements and anintermediate channel element fixed to said upper and lower elements andto the wall of said tank, said elements being of substantiallyrectangular cross section and directed alternately inwardly andoutwardly of said tank, said upper and lower elements being closed atone side thereof by the corresponding portions of the tank wall anddefining therewith upper and lower passages of substantially rectangularcross section extending substantially completely about said tank andhaving fiat walls of substantial area exposed interiorly of said tank,said channel elements being rigidly connected together and to said tankwall effective for reinforcing the latter, a duct bridging saidintermediate channel element and establishing communication between saidpassages, a baffle in said first passage closing it at one side of saidduct, and a bafile in said second passage closing it at the oppositeside of said duct, each of said passages having a coolant connectionadjacent the side of said bafile therein opposite to said duct, saidbafiies being effective for causing coolant entering one of saidpassages to flow therethrough in one direction around said tank to saidduct and through the latter to the other passage and then through saidother passage in the opposite direction around the tank to said coolantconnection of said other passage, whereby the 8 coolant flowing throughsaid one passage is preheated by heat absorbed from the solvent vaporswithin the tank before it enters said other passage.

4. In degreasing apparatus, a tank having a flat wall and adapted tocontain a degreasing solvent and vapors thereof, cooling jacket meansextending about said tank exteriorly and remote from the bottom thereof,said jacket means comprising upper and lower channel elements and anintermediate channel element fixed to said upper and lower elements andto the wall of said tank, said elements being of substantiallyrectangular cross section and directed alternately inwardly andoutwardly of said tank, said upper and lower elements being closed atone side thereof by the corresponding portions of the tank wall anddefining therewith upper and lower passages of substantially rectangularcross section extending substantially completely about said tank andhaving flat walls of substantial area exposed interiorly of said tank,said channel elements being rigidly connected together and to said tankwall effective for reinforcing the latter, a duct bridging saidintermediate channel element and establishing communication between saidpassages, a first bafile in each of said passages closing the latter andrespectively disposed at one and the same side of said duct, and asecond bafiie in each of said passages respectively disposed at theother side of said duct, said second baffle in said upper passageterminating short of the top thereof and otherwise closing said upperpassage and said second bafile in said lower passage terminating shortof the bottom thereof and otherwise closing said lower passage, each ofsaid passages having a coolant connection adjacent said first baffletherein and at the side of said first bafile opposite to said duct, saidbaffles being effective for causing coolant entering one of saidpassages to flow therethrough in one direction around said'tank to saidduct and through the latter to the other passage and then through theother passage in the opposite direction around the tank to said coolantconnection of said other passage, whereby the coolant flowing throughsaid one passage is preheated by heat absorbed from the solvent vaporswithin the tank before it enters said other passage, said second bafflesretarding flow of coolant through said passages for increased heatabsorption by the coolant.

References Cited in the file of this patent UNITED STATES PATENTSAustralia June 18, 1946

1. IN DEGREASING APPARATUS, A TANK HAVING AN ENCLOSING WALL AND ADAPTEDTO CONTAIN A DEGREASING SOLVENT AND VAPORS THEREOF, COOLING JACKET MEANSEXTENDING ABOUT VAPORS THEREOF, COOLING JACKET MEANS EXTENDING ABOUTSAID TANK EXTERIORLY AND REMOTE FROM THE BOTTOM THEREOF, SAID JACKETMEANS COMPRISING UPPER AND LOWER CHANNEL ELEMENTS AND AN INTERMEDIATECHANNEL ELEMENT FIXED TO SAID UPPER AND LOWER ELEMENTS AND TO THE TANKWALL, SAID UPPER AND LOWER CHANNEL ELEMENT BEING CLOSED AT THE INNERSIDES THEREOF BY THE CORRESPONDING PORTIONS OF THE TANK WALL DEFININGTHEREWITH UPPER AND LOWER PASSAGES EXTENDING SUBSTANTIALLY COMPLETELYYABOUT SAID TANK AND HAVING AN INNER WALL OF SUBSTANTIAL AREA EXPOSEDINTERIORLY OF SAID TANK, SAID CHANNEL ELEMENTS BEING RIGIDLY CONNECTEDTOGETHER AND SAID TANK WALL EFFECTIVE FOR REINFORCING THE LATTER, A DUCTBRIDGING SAID INTERMEDIATE CHANNEL ELEMENT AND ESTABLISHINGCOMMUNICATION BETWEEN SAID PASSAGES, EACH OF THE LATTER HVING A COOLANTCONNECTION AT THE AREA THEREOF ADJACENT SAID DUCT, AND BAFFLE MEANS INSAID PASSAGES EFFECTIVE FOR CAUSING COOLANT ENTERING ONE OF SAIDPASSAGES TO FLOW THERETHROUGH IN ONE DIRECTION AROUND SAID TANK TO SAIDDUCT AND THROUGH THE LATTER TO THE OTHER PASSAGE AND THEN THROUGH SAIDOTHER PASSAGE IN THE OPPOSITE DIRECTION AROUND THE TANK TO SAID COOLANTCONNECTION OF SAID OTHER PASSAGE, WHEREBY THE COOLANT FLOWING THROUGHSAID ONE PASSAGE IS PREHEATED BY HEAT ABSORBED FROM THE SOLVENT VAPORSWITHIN THE TANK BEFORE IT ENTERS SAID OTHER PASSAGE.